Apparatus for dry spinning cellulose acetate yarn



Feb. 15, 1944. R. M. HOFFMAN 2,341,615

APPARATUS FOR DRY SPINNING CELLULOSE ACETATE YARN Filed June 11, 1941 CELL HEATING FLUID T0 RECOVERY SYSTEM lNVENTOR.

ATTORNEY Patented Feb 15,1944

APPARATUS FOR DRY SPINNING CELLULOSE ACETATE YARN Robert M. Hoflman, E. I. du Pont de mington, DeL,

Waynesboro, Va... assignor to Nemours & Company, Wila corporation of Delaware Application June 11, 1941, Serial No. 397,629

1 Claim.

This invention relates to the manufacture of organic acid ester cellulose filaments, and more particularly to new and improved cellulose acetate filaments especially suited for use in rug pile fabric, to the process by which the filaments are formed, and to the apparatus for carrying out the process.

Processes and apparatus have heretofore been developed and successfully used for the spinning of cellulose acetate filaments of large denier, i. e., denier of and upwards to 40 denier or more.

There has also been described in the prior art, filaments of cellulose acetate which are substantially round and smooth. (By substantially round and smooth is meant that the maximum and minimum. cross-sectional dimensions at a tion.

given point are not greatly different and that the contour of the filament cross-section is relatively free of sharp indentations or crenulations.) Filaments having this substantially round and smooth cross-section do not have the capacity to hold dirt and do not become more or less permanently soiled as do filaments having highly crenulated cross-section. Furthermore, when the filaments or fibers aremore substantially round, they have improved stiffness and resilience as compared with filaments and fibers wherein the maximum cross-sectional dimension is several times, for example 10 or even times,

the minimum cross-sectional dimension.

Cellulose acetate filaments of a high degree of toughness are likewise known. In this connection it should be observed that toughness is not synonymous with tenacity. Yarn which has a high degree of toughness is not necessarily a yarn of high tenacity; in fact it may be quite the re- 'verse. For example, if a yarn has a high elongation at the breaking point even though the tenacity is lower than normal, it is apt to have a higher toughness value than a yarn of high tenacity and low elongation for the reason that more work must be done to actually rupture the yarn. Finally, cellulose acetate filaments which have a pleasing sparkle and which can be made up into a yarn having a satisfactory handle, i. e., a soft, warm, and at the same time a crisp, springy. resilient feel,. have also been described. However, while cellulose acetate filaments of the past have been characterized by one, and in some few instances several, of these properties, no cellulose acetate filament has heretofore been prepared which exhibits all of these properties, and yet, to satisfy the requirements for a filament suitable for use in rug pile, all of the enumerated properties must be present together.

These and other objects will more clearly appear hereinafter.

I have found that a filament fulfilling the requirements hereinabove stated can be produced by spinning cellulose acetate from a solution in a suitable volatile solvent by the dry or evaporative method while correlating and maintaining, in a manner to be fully explained, the following factors:

1. The concentration of the cellulose acetate in the spinning solution.

2. The temperature just prior to extrusion.

3. The temperature of the cell.

4. The concentration of the solvent vapor within the cell.

5. The size and spacing of the orifices in the spinneret.

6. The draw-off speed.

It is not necessary that any one of these factors be maintained at any specific value, but a reasonable range of values will be found satisfactory providing the other factors are suit ably adjusted although there are certain limits of conditions within which the spinning operation must be carried out to obtain satisfactory results. For instance, the concentration of solvent vapor within the cell must be kept very high if satisfactory cross-sections are to be obtained. For instance, when using acetone as the solvent the concentration of solvent vapor within the cell must be maintained above 1500 grams of acetone per cubic meter of atmosphere or above about 78% solvent vapor by volume. This is probably the most important of all the factors, but even so, unless the other factors are maintained within the limits given below, continuity of spinning cannot be maintained and/or the physical characteristics of the product produced will not be suited for use as the pile in carpets or in other floor" covering materials. The

of the spinning solution concentration of cellulose acetate in acetone or in acetone containing not more than 5% of water should be maintained within the limits of 25% to 32%. The solution temperature just prior to extrusion should be maintained within the limits of 50 C. to 70 C. The cell temperature should be maintained within the limits of from 85 C. to 115 C. The hole diameter of the oriflces of the spinning jet should be maintained within the limits of 0.10 to 0.30 millimeter. The stretch ratio, computed as the ratio of draw-01f or windup speed of the yarn to the jet velocity of the spinning solution as it issues from the orifices in the spinneret, may be varied ,quite widely, for instance from 0.8 to 6 or 7. Best results are obtained when the draw-off speed is within the range of 50 to about 150 yards per minute.

As previously pointed out, it is necessary that as one condition is varied, the other spinning conditions must also be varied to maintain a certain combination of relations with each other. Thus, with increased concentration of cellulose acetate, lower solution temperature and lower aspiration rate are desirable to compensate for the reduced amount of solvent to be evaporated. with an increased spinning speed, it is necessary to raise the cell temperature to increase the amount of solvent removed from the yarn in a given time. To compensate for these two factors (higher concentration of cellulose acetate in the spinning solution and higher spinning speed) which tend to increase the filament tension, the aspiration should preferably be kept low and the spinning solution temperature reduced. The best results at higher spinning speeds are generally obtained with higher concentration of cellulose acetate in the spinning solution.

Proper correlation of the determining factors are further illustrated by the following: In spinning a solution comprised of 28% cellulose acetate about 54% combined acetic acid), 2% water, and 70% acetone, it is preferred that the concentration of acetone vapor within the cell be maintained between 90% and 95% by volume, that the orifices within the spinneret be from 0.10 to 0.20 millimeter in diameter, that the temperature of the spinning solution just prior to extrusion be maintained at about 60 C. and the cell temperature at 89 C. (or, with a solution temperature at 55 C., the cell temperature should be maintained at 115 C.), and that the windup be maintained from 100 to 125 yards per minute. For a solution comprised of 30% cellulose acetate (about 54% combined acetic acid) and 70% acetone with or without 2 or 3% water, the following conditions are preferred. The concentration of acetone vapor within the cell should be maintained between 93% and 98% acetone by volume. Extruding the spinning solution at a temperature of about 57 C., the cell temperature should be maintained at about 90 C. (If the solution temperature is less, say 52 C., the cell temperature should be maintained at about 115 C.) To prevent filaments from sticking together in spinning in a high concentration of solvent vapor such as is described herein, it is necessary to have the orifices in the spinneret spaced at somewhat greater distance than is used for the normal method of evaporative spinning (the minimum hole spacing in a spinneret for producing a 20 filament product is about 7.5 millimeters. In spinning a larger number of filaments from one spinneret, it is desirable to have this spacing somewhat greater; for instance, in producing a 30 filament product, the hole spacing should be at least 8.0 millimeters and preferably more).

In order to regulate and maintain the various spinning conditions within the desired narrow limits, I have found it necessary to devise a radically new type of spinning cell in which to carry out the process. The structure of the spinning cell and the advantages thereof with respect to the practice of my process is best understood by reference to the accompanying drawing wherein:

Fig. 1 is a diagrammatic representation of the spinning cell in vertical cross-section together with the associated filament and solvent draw-oil elements, and

Fig. 2 is a typical cross-section of the filament produced by my process.

Referring to Fig. 1 of the drawing, I designates a metering pump which delivers the spinning solution at a constant rate to a water jacketed spinning head 2, wherein the solution is heated to the desired spinning temperature before extrusion through spinneret 3. In the spinneret assembly, a filter pack 3A of conventional design is used to develop back pressures of from 300 to 600 pounds per square inch to aid in distributing the flow of solution evenly through the holes of the spinneret and to act as a filter to prevent partial or total plugging of any of the spinneret orifices. In the upper part of the cell opposite the spinneret, a removable door 4 is provided to enable the operator to gain access to the spinneret. However, during normal operation, this opening is closed and carefully sealed to prevent the influx of any air. In the upper part of the cell also in the vicinity of the spinneret, a short pipe 5' is provided as shown to serve as a holder for an orifice 5 of from 0.0002 to 0.0012 square inch in area or, if circular, of 0.015 to 0.040 inch diameter which is used to limit the amount of air entering the cell and thu maintain a high concentration of solvent vapor in the evaporative medium in the major portion of the cell. The entire cell 8 and. especially the upper portion thereof should be well sealed to prevent influx of air other than through orifice 5 in order that the solvent vapor concentration will be precisely controlled. The main portion of the cell 6 is surrounded throughout most of its length with a heating jacket I heated by means of hot water, steam or any other suitable heating medium. At the bottom of the cell is a tube opening 8 to allow the filaments to be withdrawn. This is sufficiently small in diameter (preferably about inch) and sufficiently long (preferably about 3 to 4 inches) to permit the development of a partial vacuum of from 4; inch to 6 inches of water within the cell for the purpose of controlling the amount of air entering through orifice 5 without necessitating excessive aspiration that would cause an undesirably high gradation of acetone vapor concentration from the top to the bottom of the cell. The amount of air drawn in through opening 8 is approximately times the amount drawn through orifice 5, but since this is immediately removed and mixes with the solvent vapor only in the lowermost portion of the cell, it has no undesirable effect on the filaments being spun. .partial vacuum within the cell may be conveniently developed by means of a blower l3 which develops a partial vacuum in mixing chamber II isolated from the outside and the rest of the system by flame arresters 9 and 12. By means The . ,from the cell to dilute point below its lower explosivelimit before collecting it in the main header pipe to acetone recovery. (The acetone-air mixture in the main body of thecell-is in the upper,- non-explosive range.) The yarn after leaving the cell'through opening 8 may be conveniently taken up by mechanism l4 consisting of a yarn guide (e), a roll for finish application (a), feed roll (b), a take-up bobbin and a driving roll for the take-up bobbin ((1).

By means of the simple arrangement for regulating the influx of air into the upper part of the spinning cell, the concentration of solvent vapor in air which comprises the evaporative medium inside the cell may be easily but precisely controlled. For instance, by using a small size orifice 5, say 0.015 inch in diameter, and a slightly reduced pressure inside the cell amounting to A inch of water column, the fiow of air into the upper part of the cell will be found to be uniform and constant at about three liters per hour. By increasing the pressure difierential between the inside and the outside of the cell and the size of orifice 5, the flow of air into the upper part of the cell may be increased up to 100 liters per hour or more. The amount of air to be admitted into the upper part ofr the cell will, of course, depend upon the concentration of acetone vapor desired within the cell, the rate of spinning, the concentration of the spinning solution, the temperature of the cell, etc. If desired, instead of having orifice 5 communicating with the outside atmosphere, it may be directly connected to a source of gas other than air, for instance, an inert gas comprised of a mixture of nitrogen and carbon dioxide which may produced by any of the well known inert gas machines now on the market.

Although the means hereinbefore described for controlling the concentration of solvent vapor in the evaporative medium inside of the cell may be used very advantageously, other means as will be readily apparent to one skilled in the art can,

of course, be substituted. The only requirement is to precisely control the concentration of solvent vapor around the filaments through their major portion of their travel through the spinning cell in combination, of course, with the proper control of temperatures, draw-oil speed, and other factors previously mentioned.

To further illustrate this invention, the following examples are given, but it is not to be construed that these examples are limitative in any y.

Example! A cellulose acetate spinning solution having a viscosity of 1000 poises when measured at 40 C. and comprised of 28.5% cellulose acetate (about 54% combined acetic acid), 2.3% water, and

69.2% acetone was spun into yarn in the cell reviously described. The spinning solution l ieated at 60 C. was extruded through a 20-hole spinneret, each hole being 0.20 millimeter diameter and the holes spaced 8.0 millimeters apart.

from the cell through is much larger than ori- The inner'wall oi the jacketed portion of the cell was heated to 88 at the air intake of 0.025 inch and maintaining a slight partial vacuum inside of the cell amounting to 1% inches of water column, sufilcient air was drawn in at 37 C. to maintain an acetone concentration of 1790 grams per cubic meter (when measured at 70 C. and 760 millimeters) in the evaporative medium in the cell or 93.4% of acetone by volume. The extrusion rate of the spinning solution was up speed of 125 yards per minute, a 400 denier, filament yarn was produced.

The yarn so produced, after conditioning at a constant'humidity of 65% R. H. and a temperature of. 75 F., had a dry strength of 1.00 gram per denier and a dry elongation at the breaking point of 47% as measured on a Scott inclined tester. The cross-sectional ments was peanut-shaped (see Fig. 2) with the I natured alcohol in water.

. pleasing minimum diameter of: an average cross-section about 30% of the maximum diameter of the average cross-section. The contour of the crosssection was generally smooth. The yarn had a handle,-good uniformity, and could be satisfactorily handled on textile machinery. When woven as the pile in carpet. it was found to have the desired resilience and other desirable characteristics needed in this type fabric.

A simple test which distinguishes my yarn from large denier yarns spun according to the usual procedures is carried out as follows: A sample of the yarn of this example is soaked for two minutes in 70% denatured alcohol at 15 C. and stretched 25%, washed in water, dried, and is then immersed in a boiling solution of 10% detreatment, the yarn spontaneously elongates at least 25%. Known large denier yarns do not respond in this fashion.

' Example II viscosity of 400 poises cellulose acetate (having an acetic acid content of about 54%) and acetone was spun into 200 denier, 10 filament yarn using this same type spinning cell. In this case thespinning solution temperature was 70 0., the cell temperature 88 C., and sufiicient air was drawn into the upper part of thecell through orificei to maintain an average acetone concentration of 1850 grams per cubic meter or about 96.3% of acetone by volume (measured at 70 C. and 760 millimeters). The diameter of the spinneret orifices was 0.17 millimeter spaced 7.5 millimeters apart and with a windup speed of yards per minute, the stretch ratio was 2.3. The yarn so produced had a dry strength of 1.26 grams per denier and a dry elongation of 56% when conditioned and measured at 65% R. H. and at 75 F. The cross-section was substantially the same as shown responded to the spontaneous elongation test of Example I.

Example III through a 20-hole spinneret, the holes being 0.3

' millimeter diameter, into the cell previously described which cell body was heated to a tempera- C. The evaporative atmosphere contained an average acetone conture of within the cell C. and using an orifice (5) such that with a windshape of the fila- As a result of this A cellulose acetate spinning solution having a in Fig. 2 and the yarn centration of 1820 grams per cubic meter or about 95% of acetone by volume (measured at 70C. and 760 millimeters). With the windup speed the same as in Example II, i. e., 100 yards per minute, the production of a 400 denier, filament yard necessitated the same rate of solution delivery through each orifice,- but in view of the much larger size openings in the spinneret (the area being more than three times that given under Example II), the jet velocity was less than or the stretch ratio was about 7.3. The characteristics of the yarn so produced were generally the same as in Example I, the dry tenacity of the yarn being 0.98 gram per denier, the dry elongation 51% and the filament cross-sections similar to that shown in Fig. 2.

Example IV The Spinning solution described under Example II heated to 60 C. was extruded through a 20- hole spinneret, the diameters of the holes being Example V A spinning solution was prepared by mixing together parts of cellulose acetate (about 54% combined acetic acid), 2 parts of water and 68 parts of acetone and the viscosity of the solution as measured at C. was found to be 1500 poises. The solution (after filtration, resting, etc.) Was heated to 60 C. and was extruded through a spinneret having 20 holes, each hole being 0.12 millimeter diameter, into the spinning cell previously described and heated to 88 C. while maintaining an average concentration of 1810 grams of acetone per cubic meter orabout 94.3% of acetone by volume (measured at 70 C. and 760 millimeters) as the evaporative medium inside the cell. The rate of extrusion was so adjusted that at a windup of 125 yards per minute, the yarn had a final denier of 400. In this case, the stretch ratio was 1.4.

The yarn so produced had a dry tenacity of 1.20 grams per denier, a dry elongation of 51% and a cross-section very similar to that of Fig. 2.

Example VI The spinning solution of Example V heated to 55 C. was extruded through a spinneret with twenty 0.20 millimeter holes in the spinning cell of this invention heated to 115 C. and containing suflicient air so that a concentration of 1870 grams of acetone per cubic meter or 97.4% of acetone by volume was maintained as the evaporative medium. The solution delivery rate was adjusted to yield a 400 denier yarn at a drawoff speed at 150 yards per minute which resulted in a stretch ratio of 3.9. The yarn so produced had a dry tenacity of 0.95 gram per denier, a dry elongation of 41% and a cross-section as shown in Fig. 2.

Example VII A cellulose acetate spinning solution comprising 25% cellulose acetate (having about 54% combined acetic acid) and 75% acetone and a viscosity of 400 poises measured at 40 C. was heated to 68 C, and extruded through a 10-hole spinneret, each hole being 0.14 millimeter diameter and spaced 10 millimeters apart, into the spinning cell of this invention which was heated to 88 C. while the evaporative medium therein was maintained at a concentration of 1710-grams of acetone per cubic meter or about 89.0% of acetone by volume (measured at 70 C. and 760 millimeters). The solution delivery rate was adjusted to yield a 200 denier, 10 filament yarn at a. windup speed of 114 yards per minute. The stretch ratio was 1.6. The yarn so produced by this example had a dry tenacity of 1.26 grams per denier, a dry elongation of 44% and filament cross-section very similar to Fig. 2.

While my invention is described primarily from the standpoint of spinning acetone-soluble cellulose acetate from an acetone solution or an acetone-water solution, the invention is also applicable to the dry spinning of cellulose acetate of the same or different combined acetic acid content dissolved in any one or more of the wellknown volatile solvents for cellulose acetate. Also, in place of the cellulose acetate, other cellulose organic esters may be similarly spun into yarn from a suitable solution of volatile solvents; for instance, yarns of cellulose propionate, cellulose butyrate, cellulose aceto-propionate, cellulose aceto-butyrate, etc., may be produced.

By means of my invention, filaments or fibers having the characteristics desired for use as the pile in carpet or like materials such as set forth earlier in this description can be readily produced. The spinning cell of this invention enables uniform spinning conditions to be maintained over long periods of time, and whenever a different yarn (filament size or count, for example) is desired a change in spinning conditions can be effected easily. Even though a number of important factors are involved and maintaining these factors within exceedingly narrow limits for any given production is essential, filaments having the desired uniform characteristics are readily produced.

Not only does my invention satisfy all the essential requirements for a good carpet pile filament or fiber, but under these preferred conditions, a yarn having large denier filaments shaped in cross-section like a peanut, a pinched in ellipse, or even at times bean-shaped or elliptical and with a relatively smooth contour can be produced which has a characteristic sparkle, a high degree of toughness, and an altogether satisfactory "handle. When these filaments or fibers are incorporated as the pile in rugs or carpets, they very materially enhance the appearance of the rug or carpet.

It is to be understood of course that the above description is for purposes of illustration only, and that my invention is not limited to the exact conditions and structure herein set out but is subject rather to all variations and modifications falling within the terms and spirit thereof as defined in the following claim.

I claim:

Apparatus for dry-spinning filaments from a solution of cellulose acetate comprising a spinning cell, a spinneret having a plurality of uniformly sized circular orifices of from 0.10 to 0.30 mm. in diameter located at one end of the cell, an outlet tube for filaments located at the opposite end of the cell, a circular gas inlet orifice of from 0.015 to about 0.040 inch in diameter located into the mixing chamber and thence to a solvent recovery system, all of the openings in said cell and in said mixing chamber being so related in size as to permit the maintenance of a partial 5 vacuum of from A; to 6 inches of water within said cell.

ROBERT M. HOFFMAN. 

